The invention relates to an arrangement for connecting an operating instrument with an electromotor driving instrument and a machine tool with a driving shaft protruding from the driving device and a coupling part on the operating device receiving the driving shaft.
Customarily, machine tools are produced either as compact motor devices, or else as so-called adapter devices, where the operating device, f. ex. a circular saw, a grinding device, a compass saw etc., is built on the spindle collar of a driving device normally serving as a hand drill and is driven by means of a hexagon or a flat blade by way of a drilling spindle. Compact motor devices are expensive, since a separate motor and a separate gearing must be provided for each operating device. However, the adapter devices which are altogether cheaper do have considerable disadvantages, to wit:
(a) The attachment and removal of the pertinent operating device from the driving device is so cumbersome that even after a short time in most cases the possibility of exchanging the operating device is no longer used. The connecting of an operating device to the driving device is difficult and time consuming especially because it is not simple to make the two coupling parts intermesh.
(b) Coupling is accomplished in the case of the known devices by means of a polygon on the drilling spindle which polygon engages with the corresponding coupling recess of the operating device. This coupling is flattened relatively quickly, so that considerable play develops since the mutual centering of the driving device and the operating device is very complicated. The operating device is aligned exclusively by means of the spindle collar of the driving device, f. ex. of the drill. In the case of tightening the clamping ring of the operating device, eccentricities develop perforce which lead to the above mentioned damage of the coupling in the course of time and which are the cause of strong coupling noises.
(c) Because of the eccentricities mentioned under (b), the bearings in the area of the coupling can be loaded unilaterally which leads to an increased bearing friction and consequently to a quicker deterioration.
(d) The known kind of connection between the operating device and the driving device leads to large overall construction lengths, which make the machine tool awkward. For this reason, compact devices, where the motor, the gearing and the operating device are frequently preferred despite their considerably higher procurement cost.